Zinc-air electrochemical cells are finding increasing use in small devices, such as hearing aids. These devices are trending toward higher drain rates and/or higher functional end point voltages, at least partially in response to increased usage of wireless protocols and a more competitive landscape fueled by a growing population of people who need hearing aids.
Zinc-air batteries rely on oxygen from the atmosphere to act as the cathode reactant. The air diffuses into the cell through an air electrode structure that catalytically promotes the reduction of oxygen in the presence of an aqueous electrolyte. The resulting cell possesses a high energy density, owing to the fact that only one electrode material (zinc) must be provided, but relatively low power output/rate capability. Also, the reliance upon ambient air means that once the air electrode structure is exposed, the cell may dry out.
One of the challenges in designing zinc-air batteries relates to the multiplicity of potential components in both the positive (air) and negative (zinc) electrodes which can influence the overall performance of the cell, both in terms of capacity and rate capability. In the air electrode, a failure to properly engineer the external face (i.e., the side of the electrode exposed to the ambient atmosphere) with sufficient hydrophobic properties could lead to unwanted moisture “flooding” the electrode surface and impeding performance, whereas a corresponding absence of hydrophilicity on the opposing, internal side could impede the mechanisms necessary for the electrochemical reaction to proceed at an optimal rate. In the zinc electrode, gassing, passivation and/or other unwanted interactions between the active and inactive components can have deleterious effects. In both cases, the use of inactive additives and components to potentially mitigate these effects must be balanced against the desired performance traits, insofar as inactive components occupy volume in the cell that could otherwise be devoted to active material(s).
Many past attempts at improving zinc-air cell performance have focused on a single component or single additive. In doing so, these solutions often failed to consider or acknowledge the corresponding, and sometimes negative, effects that these single component/additive solution have on the other aspects of the cell design.
The following description and the drawings disclose various illustrative aspects. Some improvements and novel aspects may be expressly identified, while others may be apparent from the description and drawings.